1. Field of the Invention
The invention relates to an objective having at least one optical element that is mounted in an inner mount, the inner mount being connected to an outer mount, and having a manipulator device for translatory displacement of the optical element in at least one direction. The invention relates in particular to a projection lens for microlithography for the purpose of producing semiconductor devices.
2. Description of the Related Art
In objectives, in particular projection lenses of projection exposure machines, it is necessary to displace individual optical elements such as, for example, lenses, in order to remove aberrations with reference to the remaining optical elements. This adjustment can be performed as a translatory displacement parallel to the optical axis, or else transverse to it. Known for this purpose are manipulator devices or actuators that displace an inner mount, in which the optical element is mounted, with reference to an outer mount. Reference may be made here to, for example, DE 198 59 634 A1 and DE 199 01 295.
However, there is a problem with these displacements that it is not always ensured that a purely translatory or linear displacement occurs. Rather, it is also possible for tilting movements and/or displacements transverse to the desired direction to occur. Moreover, a translatory movement is intended to be performed along or parallel to the desired direction with as little friction as possible, in order to avoid hysteresis effects.
It is therefore the object of the present invention to create an objective in which individual optical elements to be displaced can be displaced in a fashion as free from friction as possible, in particular along or parallel to the optical axis, the aim being the occurrence of no tiltings, as far as possible, and no displacements in other directions than the desired direction.
This object is achieved according to the invention by virtue of the fact that at least one elastically deformable strip is arranged in a gap between the inner mount and the outer mount, the strip being connected in each case via a fastening section to the inner mount and the outer mount, and the two fastening sections being connected to one another by an arcuate section and free hearing parts situated therebetween.
A preferred embodiment is represented in this case by a projection lens for microlithography for the purpose of producing semiconductor devices.
Owing to the elastically deformable strip arranged between the inner mount and the outer mount, a purely translatory displacement of the inner mount with reference to the outer mount is performed parallel to or along the optical axis. This is effected by virtue of the fact that the free bearing parts of the elastic strip can each roll on the associated circumferential wall, the inner mount also simultaneously being displaced in the purely translatory or linear fashion relative to the outer mount via the fastening sections.
In a preferred embodiment of the invention, it is possible here for the strip to be provided in each case with two arcuate sections and free bearing parts situated therebetween. A closed rolling strip with an exact translatory movement is produced when in this case the arcuate sections, the fastening sections and the free bearing parts are in one piece.
In a further preferred embodiment, the inner mount is constructed as an inner ring and the gap is constructed as an annular gap in which a plurality of rolling strips are arranged distributed over the circumference. At least the side of the outer mount facing the inner ring should likewise in this case have an annular shape.
In order to achieve a bearing surface that is as even as possible and therefore good, the inner ring and the outer mount can be provided in the region of the annular gap with flat spots, and the rolling strips can be provided at the sites of the flat spots.
In general, it will be sufficient to arrange three rolling strips distributed uniformly over the circumference in the annular gap. However, in order to increase the stiffness, it is also possible, of course, to arrange more than three rolling strips, for example four rolling strips, in which case two rolling strips should be arranged opposite one another in each case.
Advantageous refinements and developments of the invention emerge from the subclaims and from the following exemplary embodiment described in principle with the aid of the drawing, in which: